Question about engines and resource consumption/production

[Crimsonraziel]

I tried to create an engine that is using some "charged" resource and turns it into gas(thrust) some "uncharged" version of that resource. (The basic idea is to recharge that "uncharged" resource with energy and some gas on planets with atmosphere or something like that.)

So I need an engine that not only consumes some resources, but also produces some waste resource.

At first I tried to use 'ModuleAlternator' but it seems the calculation for this works different and I couldn't balance that the way I wanted to. For every 1 "charged" resource used by the engine there should be 1 produced "uncharged" resource.

I tried another approach by adding the "uncharged" resource as propellant and giving it a negativ ratio (charged resource ratio 1, uncharged -1).

At first I thought it worked out, but then I ended up with 60.17 units produced out of 60 units, which means after recharging I would have more fuel than I started with. That's not intended^^

How can I make it match exactly? I don't really care if I use it as propellant for ModuleEngines or as resource for ModulAlternator as long as the numbers work out. Any suggestions?